Method and apparatus for image processing, and a computer product

Abstract

In the image processing apparatus a matrix selector selects a position matrix for determining the gradation direction. The gradation direction is the direction of a contrast of a gradation at a position of a target pixel and a dispersion matrix for determining a spatial frequency at the position of the target pixel. Further, a pixel interpolator divides the target pixel into still smaller pixels. A table selector selects a conversion table for determining a gradation level of the smaller pixels based on the gradation level of the target pixel, the position matrix and the dispersion matrix.

What is claimed is:  
     
       1. An image processing apparatus which varies resolution of an image and a gradation level of the pixels composing the image, the image processing apparatus comprising: 
       a gradation direction determining unit which determines a gradation direction which is a direction of a contrast of the gradation at the pixel position of a target pixel;  
       a spatial frequency determining unit which determines a spatial frequency at the pixel position of the target pixel;  
       a dividing unit which divides the target pixel into fine pixels; and  
       a gradation determining unit which determines a gradation level of the fine pixel produced by the dividing unit based on the gradation level of the target pixel, the gradation direction determined by the gradation direction determining unit and the spatial frequency determined by the spatial frequency determining unit.  
     
     
       2. The image processing apparatus according to  claim 1 , wherein the spatial frequency determining unit determines the spatial frequency at the pixel position of the target pixel based on the type of the image. 
     
     
       3. The image processing apparatus according to  claim 1 , wherein the dividing unit bisects or quadrisects the target pixel. 
     
     
       4. The image processing apparatus according to  claim 1  further comprising: 
       a gradation varying unit which varies the gradation level of the target pixel to a gradation level in a range narrower than that of the gradation level.  
     
     
       5. The image processing apparatus according to  claim 4 , wherein the gradation varying unit compares the gradation level of the target pixel with a predetermined threshold, so as to vary the gradation level of the target pixel. 
     
     
       6. The image processing apparatus according to  claim 4 , wherein the gradation varying unit varies the gradation level of the target pixel by the use of a predetermined dither matrix. 
     
     
       7. An image processing apparatus according to  claim 6 , wherein the gradation determining unit determines a gradation level of the fine pixel produced by the dividing unit based on the dither matrix and the element position of the dither matrix. 
     
     
       8. An image processing apparatus which varies resolution of an image and a gradation level of the pixels composing the image, the image processing apparatus comprising: 
       a gradation direction determining means for determining a gradation direction which is a direction of a contrast of the gradation at the pixel position of a target pixel;  
       a spatial frequency determining means for determining a spatial frequency at the pixel position of the target pixel;  
       a dividing means for dividing the target pixel into fine pixels; and  
       a gradation determining means for determining a gradation level of the fine pixel produced by the dividing means based on the gradation level of the target pixel, the gradation direction determined by the gradation direction determining means and the spatial frequency determined by the spatial frequency determining means.  
     
     
       9. The image processing apparatus according to  claim 8 , wherein the spatial frequency determining means determines the spatial frequency at the pixel position of the target pixel based on the type of the image. 
     
     
       10. The image processing apparatus according to  claim 8 , wherein the dividing means bisects or quadrisects the target pixel. 
     
     
       11. The image processing apparatus according to  claim 8  further comprising: 
       a gradation varying means for varying the gradation level of the target pixel to a gradation level in a range narrower than that of the gradation level.  
     
     
       12. The image processing apparatus according to  claim 11 , wherein the gradation varying means compares the gradation level of the target pixel with a predetermined threshold, so as to vary the gradation level of the target pixel. 
     
     
       13. The image processing apparatus according to  claim 11 , wherein the gradation varying means varies the gradation level of the target pixel by the use of a predetermined dither matrix. 
     
     
       14. An image processing apparatus according to  claim 13 , wherein the gradation determining means determines a gradation level of the fine pixel produced by the dividing means based on the dither matrix and the element position of the dither matrix. 
     
     
       15. An image processing method of varying resolution of an image and gradation level of the pixels composing the image, the image processing method comprising the steps of: 
       determining a gradation direction which is a direction of a contrast of the gradation at the pixel position of a target pixel;  
       determining a spatial frequency at the pixel position of the target pixel;  
       dividing the target pixel into fine pixels; and  
       determining a gradation level of the fine pixel produced in the dividing step based on the gradation level of the target pixel, the gradation direction determined in the gradation direction determining step and the spatial frequency determined in the spatial frequency determining step.  
     
     
       16. The image processing method according to  claim 15  further comprising the step of: 
       varying the gradation level of the target pixel to a gradation level in a range narrower than that of the gradation level.  
     
     
       17. A computer readable medium for storing instructions, which when executed by a computer, causes the computer to perform the steps of: 
       determining a gradation direction which is a direction of a contrast of the gradation at the pixel position of a target pixel;  
       determining a spatial frequency at the pixel position of the target pixel;  
       dividing the target pixel into fine pixels; and  
       determining a gradation level of the fine pixel produced in the dividing step based on the gradation level of the target pixel, the gradation direction determined in the gradation direction determining step and the spatial frequency determined in the spatial frequency determining step.